Narrow grass hedge effects on phosphorus and nitrogen in runoff following manure and fertilizer application

ABSTRACT:

Runoff losses of nitrogen (N) and phosphorus (P) from field applied manure can contribute to surface water pollution. Grass hedges may reduce runoff losses of nutrients and sediment. The objective of this study was to evaluate the effects of narrow switchgrass (Panicum virgatum L.) hedges (−0.75 m wide) on the transport of P and N from a field receiving beef cattle feedlot manure under tilled and no-till conditions. This study was conducted on a steep (12 % average slope) Monona silt loam (fine-silty, mixed, superactive, mesic Typic Hapludolls) soil near Treynor, Iowa. The experiment was a split-plot with no-till and disked systems as main plots and subplots of manure, fertilizer, and check with or without a grass hedge. A rainfall simulator was used and runoff was collected from both the initial and the following wet simulations. Only 38% of the no-till plots and 63% of disked plots had any runoff during the initial 6.4 cm hr⁻¹ water application. A single narrow grass hedge reduced runoff concentrations of dissolved P (DP) by 47%, bioavailable P (BAP) by 48%, particulate P (PP) by 38%, total P (TP) by 40%, and NH₄-N by 60% during the wet simulation on the no-till plots receiving manure, compared with similar plots with no hedges. The corresponding reductions in concentrations as a result of a grass hedge for DP, BAP, PP, TP, and NH₄-N on the disked plots were 21, 29, 43, 38, and 52%, respectively. Runoff NH₄-N concentration from fertilizer applied to the disked plots was reduced by 61%, NO₃-N by 21%, and total N (TN) by 27% during the wet simulation when grass hedges were used. Grass hedges also reduced total quantities of DP, BAP, TP, and NH₄-N during the wet simulation. The TP loss was 3.3% of applied P fertilizer and was 0.3% of applied manure P. Narrow grass hedges were effective in reducing P and N losses in runoff from both manure and fertilizer application.